Light, dust, contradiction, an absurd remark, the sight of a Dissenter -- anything sets me sneezing; and if I begin sneezing at twelve, I don't leave off till two o'clock, and am heard distinctly in Taunton, when the wind sets that way -- a distance of six miles. -- Sydney Smith, 1835.

If you're not sneezing at this time of year, count your blessings.

On the street, in the subway and in the garden, people are exhaling with explosive fury. For those with allergies, the season declares war on the senses, shell-shocking the sinuses and booby-trapping the eyes with exploding tears. The nose, out of self-defense, becomes a rocket launcher.

One Washington allergist had a patient who was going through four boxes of tissues a day. Another tells of a man whose sneezing fit grew so bad it drove him and his date from a restaurant in the middle of their meal. A third recalls cases in which sneezing due to cat allergies drove one couple from the altar and another to a divorce court.

That some accuse Washington of being the sinus capital of the nation is attributed by allergists to the city's aggravating combination of pollen, humidity and pollutants.

"We have a long pollen season here in Washington," says Dr. Richard R. Rosenthal, chief of the allergy section at Fairfax Hospital and assistant professor at the Johns Hopkins School of Medicine. "We've lots of reason to be sneezing."

He cites pollen, mold spores, dust mites, animal dander (particularly from cats) and cigarette smoke as contributing factors. As the body goes into its defensive mode to get rid of these irritants, a sneeze erupts.

Here's what happens: Membranes in the nose swell up and secrete a liquid, creating a ticklish sensation. A respiratory phase follows in which the lungs fill with air. You can still stop a sneeze in its tracks at this stage by limiting the amount of air. Once a breath is completed, the expulsion is imminent.

The How is clear to doctors; more confusing is the Why.

"We know what sneezing is and how the whole muscular contraction takes place, but we don't know how the other factors are involved," says Dr. Alkis Toyas, a fellow in allergy and clinical immunology at Johns Hopkins.

Researchers speculate that numerous factors can spark an outburst: foul odors, pregnancy, menstruation, sudden contact to bright light, and such emotions as resentment, grief, frustration and joy.

"There are many substances, says Toyas, "that are secreted in the brain and other tissues in the body that have been related to emotional factors. These substances are capable of stimulating nerves. Thus it is possible they can stimulate the specific nerves that cause sneezing. "

Even sexual arousal may be a sneeze factor.

"The nose is a very sensitive organ, so it's not that unusual," says Dr. I. Leonard Bernstein, an allergist-immunologist at the University of Cincinnati School of Medicine. "The tissue in the nose resembles tissues involved in sex; there are increased numbers of blood vessels and nerve fibers."

Responding to a blast with "God bless you" or "Gesundheit" is almost as compelling as the necessity to sneeze itself. "The phrases are a reflex, just like the sneeze," says Rosenthal.

Most people were instructed to excuse themselves after yawning, coughing or burping, but it's unlikely that anyone ever taught you to bless others after they sneeze. In this respect the sneeze transcends a mere bodily function, moving into the realm of the spiritual.

Greek mythology says the sneeze originated when Prometheus stole a sunbeam in an effort to bring to life a statue he created. To hide the light from sun god Apollo, Prometheus placed the beam in his snuff box and later mistook it for snuff. This inadvertent oversight set Prometheus into a violent nasal fit, and the sneeze was born.

The Christian term "God bless you" apparently originated in the 6th century, when Saint Gregory uttered the phrase during a plague in which sneezing indicated a person had a fatal disease. Gesundheit -- German for "health" -- is a variation of that. Both expressions have stuck.

Sneezing has always been considered a fit topic for philosophy. Pascal said that it "absorbs all the faculties of the soul," while Montaigne observed: "We produce three sorts of wind: that issuing from below is too undecent; that from the mouth implieth some reproach of gourmandise; the third is sneezing; and because it cometh from the head, and is without imputation, we thus kindly entertain it."

Other cultures have also accorded sneezing a special place in their respective folklore. In Tonga, to sneeze before a journey means bad luck; in Jamaica, it's a clue someone's saying bad things about you; among Hindus, a sneeze provides spirits a passage in and out of the body; Zulus thank each other when they sneeze. In Germany, it's bad luck to sneeze while putting on your shoes, but if one occurs during a conversation it means the last statement was true. A more worrisome bit of folklore holds that the heart stops during a sneeze, and, because death is so near, you need a blessing.

But it is just a myth. "A deep respiratory maneuver such as a sneeze reflexively slows the heart momentarily but really has no life-threatening significance," says Rosenthal.

More alarming are the cases of chronic sneezers. The Guinness Book of World Records gives the title to Donna Griffiths, an English girl who started sneezing on Jan. 13, 1981. On her 195th day she surpassed the previous record. Donna sneezed an estimated million times in the first 365 days; not for 32 months did she have her first sneeze-free day.

Will there ever be an end to sneezing?

"No. I think it's part of the human condition," Rosenthal says. "People will always need something to sneeze at."